Bushing type vibration insulator - Patent Review 4858899

What is claimed is:

1. A bushing type vibration insulator which insulates vibrations in an automotive vehicle, comprising:

an outer cylindrical member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member;

said inner and outer cylindrical members sharing a common central longitudinal axis;

an elastic member disposed between said outer and inner cylindrical members to connect said outer and inner cylindrical members;

means defining at least two fluid chambers filled with a fluid, said fluid chambers being located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of said elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers;

an electrically operated actuator constructed and arranged to close said first communication passage to block fluid communication between said fluid chambers under a predetermined condition, said actuator being fixedly secured directly to said outer cylindrical member.

2. A bushing type vibration insulator as claimed in claim 1, wherein said elastic member is formed with at least two grooves which respectively define therein said fluid chambers, each groove being sealingly covered with inner peripheral surface of said outer cylindrical member.

3. A bushing type vibration insulator as claimed in claim 1, further comprising an intermediate cylindrical member disposed between said outer and inner cylindrical members, wherein said elastic member is securely connected to said intermediate cylindrical member which is securely connected to said outer cylindrical member.

4. A bushing type vibration insulator as claimed in claim 3, wherein a major part of said intermediate cylindrical member is embedded in said elastic member and located near said outer cylindrical member, wherein a thin layer of said elastic member is located between said intermediate and outer cylindrical members.

5. A bushing type vibration insulator as claimed in claim 1, wherein said actuator includes a body in which a first portion of said communication passage is formed, said body being fixedly secured to a part of said vibration insulator, and a spool constructed and arranged to close said part of said first communication passage in response to said predetermined condition.

6. A bushing type vibration insulator as claimed in claim 1, further comprising means for allowing the fluid to flow through said first communication passage even under a condition where vibration having frequency higher than a predetermined level is transmitted to said vibration insulator, said fluid flow allowing means including means for increasing rigidity of said elastic member.

7. A bushing type vibration insulator as claimed in claim 6, further comprising an intermediate cylindrical member disposed between said outer and inner cylindrical members, wherein said elastic member rigidity increasing means includes a reinforcement ring embedded in said elastic member and located between said inner cylindrical member and said intermediate cylindrical member, said reinforcement ring being generally coaxial with said inner cylindrical member.

8. A bushing type vibration insulator as claimed in claim 6, wherein said elastic member has opposite end sections in axial direction, said opposite end sections defining therebetween one of said fluid chambers and formed into the shape of a diaphragm, wherein said elastic member rigidity increasing means includes reinforcement cords embedded in each of said opposite end sections of said elastic member.

9. A bushing type vibration insulator as claimed in claim 1, further comprising means for reducing amount of relative displacement between said outer and inner cylindrical members even under said predetermined condition.

10. A bushing type vibration insulator as claimed in claim 9, wherein said relative displacement amount reducing means includes means defining a second communication passage for establishing fluid communication between said fluid chambers, said second communication passage being smaller in cross-sectional area than said first communication passage.

11. A bushing type vibration insulator as claimed in claim 9, wherein said relative displacement amount reducing means includes first means for detecting amount of relative displacement between said outer and inner cylindrical members, second means for comparing the detected relative displacement amount with an allowable range of said relative displacement, and third means for closing said communication passage when the detected relative displacement amount is within said allowable range.

12. A bushing type vibration insulator which insulates vibrations in an automotive vehicle, comprising:

an outer cylindrical member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member;

an elastic member disposed between said outer and inner cylindrical members to connect said outer and inner cylindrical members;

means defining at least two fluid chambers filled with a fluid, said fluid chambers located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of said elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers;

an electrically operated actuator constructed and arranged to close said first communication passage to block fluid communication between said fluid chambers under a predetermined condition, said actuator being fixedly secured to said outer cylindrical member;

said actuator including a body in which a first portion of said first communication passage is formed, said body being fixedly secured to a part of said vibration insulator, and a spool constructed and arranged to close said first portion of said first communication passage in response to said predetermined condition;

said first portion of said first communication passage having first and second ends;

said first communication passage defining means including means defining a second portion of said first communication passage, formed through a wall of said outer cylindrical member and communicated with said one of the first and second ends of said first communication passage first portion, and means for defining a third portion of said first communication passage, formed between said outer and intermediate cylindrical members and communicated with one of said fluid chambers.

13. A bushing type vibration insulator which insulates vibrations in an automotive vehicle, comprising:

an outer cylindrical member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member;

an elastic member disposed between said outer and inner cylindrical members to connect said outer and inner cylindrical members;

means defining at least two fluid chambers filled with a fluid, said fluid chambers being located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of said elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers;

an electrically operated actuator constructed and arranged to close said first communication passage to block fluid communication between said fluid chambers under a predetermined condition, said actuator being fixedly secured to said outer cylindrical member;

said actuator including a body in which a first portion of said communication passage is formed, said body being fixedly secured to a part of said vibration insulator, and a spool constructed and arranged to close said first portion of said first communication passage in response to said predetermined condition;

further comprising a cylindrical bracket inside which said outer cylindrical member is fixedly secured;

said first portion of said communication passage having first and second ends;

said communication passage defining means including second and third portions of said communication passage, formed through a wall of said cylindrical bracket and respectively communicated with the first and second ends of said communication passage first portion, said third portion being communicated through said outer cylindrical member with one of said fluid chambers, and means for defining a fourth portion of said communication passage, formed between said cylindrical bracket and said outer cylindrical member, said fourth portion having first and second ends, said fourth portion first end being communicated with second portion, said fourth portion second end being communicated through said outer cylindrical member with another one of said fluid chambers.

14. A bushing type vibration insulator as claimed in claim 13, further comprising an O-ring disposed between said cylindrical bracket and said outer cylindrical member and located between said second and third portions of said communication passage.

15. A bushing type vibration insulator as claimed in claim 5, wherein said communication passage is formed through said inner cylindrical member, wherein said actuator spool is located within a bore of said inner cylindrical member and rotatable to close said communication passage first portion in response to said predetermined condition.

16. A bushing type vibration insulator as claimed in claim 5, where said spool is formed with a first through-opening which is capable of being coincident with said communication passage first portion to allow the fluid to flow through said communication passage first portion, said first through-opening being put out of said communication passage first portion to prevent the fluid from flowing through said communication passage first portion under a first predetermined condition.

17. A bushing type vibration insulator as claimed in claim 16, said spool is further formed with second through-opening which is capable of being coincident with said communication passage first portion, said second through-opening being put out of said communication passage first portion under a second predetermined condition, said second through-opening being smaller in cross-sectional area than said first through-hole.

18. A bushing type vibration insulator as claimed in claim 3, further comprising a cylindrical bracket inside which said outer cylindrical member is fixedly secured, wherein said intermediate cylindrical member is formed with a small diameter section to which an end section of said outer cylindrical member securely fit to form a space between a larger diameter section of said intermediate cylindrical member and said cylindrical bracket, a sealing material being disposed among said intermediate cylindrical member large diameter section, said outer cylindrical member and said cylindrical bracket.

19. A bushing type vibration insulator as claimed in claim 5, wherein said actuator body is fixedly secured to said outer cylindrical member.

20. A bushing type vibration insulator which insulates vibrations in an automotive vehicle, comprising:

an outer member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member;

an elastic member disposed between said outer and inner cylindrical members to connect said outer and inner cylindrical members;

means defining at least two fluid chambers filled with a fluid, said fluid chambers being located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of said elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers;

an electrically operated actuator constructed and arranged to close said first communication passage to block fluid communication between said fluid chambers under a predetermined condition, said actuator being fixedly secured to said outer cylindrical member;

said actuator including a body in which a first portion of said first communication passage is formed, said body being fixedly secured to a part of said vibration insulator, and a spool constructed and arranged to close said first portion of said first communication passage in response to said predetermined condition; and

further comprising a cylindrical bracket inside which said outer cylindrical member is fixedly secured, and a hollow rod fixedly secured to said cylindrical bracket, wherein said actuator body is disposed inside said rod and fixedly secured to said cylindrical bracket.

21. A bushing type vibration insulator as claimed in claim 11, wherein said first, second, and third sections of said relative displacement amount reducing means are incorporated as a unit to form a displacement sensor, said displacement sensor being fixedly secured to said actuator.

22. A bushing type vibration insulator as claimed in claim 1, wherein said at least two fluid chambers defining means includes means for defining two fluid chambers which are located diametrically opposite to each other.

23. A bushing type vibration insulator as claimed in claim 22, wherein said two fluid chambers are located symmetrical to each other with respect to said inner cylindrical member.

24. A bushing type vibration insulator which insulates vibrations in an automotive vehicle, comprising:

an outer cylindrical member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member;

said inner and outer cylindrical members sharing a common central longitudinal axis;

an elastic member disposed between said outer and inner cylindrical members to connect said outer and inner cylindrical members;

means defining at least two fluid chambers filled with a fluid, said fluid chambers being located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of said elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers;

an electrically operated actuator constructed and arranged to be put into a first state to close said first communication passage to block communication between said fluid chambers, and into a second state to open said first communication passage to establish the fluid communication, said actuator being fixedly secured directly to said outer cylindrical member; and

means for putting said actuator into said first state during high speed cruising of the vehicle, and into said second state during rough road cruising of the vehicle.

25. A bushing type vibration insulator which insulates vibrations in a suspension of an automotive vehicle comprising:

an outer cylindrical member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member;

said inner and outer cylindrical members sharing a common central longitudinal axis;

an elastic member disposed between said outer and inner cylindrical members to connect said outer and inner cylindrical members;

means for transmitting vibration to cause relative displacement between said outer and inner cylindrical members through said elastic member;

means defining at least two fluid chambers filled with a fluid, said fluid chambers being located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of said elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers;

an electrically operated actuator constructed and arranged to be put into a first state to close said first communication passage to block fluid communication between said fluid chambers, and into a second state to open said first communication passage to establish the fluid communication, said actuator being fixedly secured directly to said outer cylindrical member; and

means for putting said actuator into said first state during high speed cruising of the vehicle, and into said second state during rough road cruising of the vehicle.

26. A bushing type vibration insulator which insulates vibrations in an automotive vehicle, comprising:

an outer cylindrical member;

an inner cylindrical member disposed inside and spaced from said outer cylindrical member, said inner and outer cylindrical members sharing a common central longitudinal axis;

an elastic member disposed between said outer and inner cylindrical members;

means defining at least two fluid chambers filled with a fluid, said fluid chambers being located between said outer and inner cylindrical members and separate from each other in peripheral direction of said outer and inner cylindrical members, said fluid chambers defining means including a part of elastic member;

means defining a first communication passage for providing fluid communication between said fluid chambers; and

an electrically operated actuator constructed and arranged to close said first communication passage to block fluid communication between said fluid chambers under a predetermined condition, said actuator being secured directly to said outer cylindrical member, said actuator including a body in which a first portion of said communication passage is formed, said body being fixedly secured to said outer cylindrical member, and an electrically operated and axially movable spool disposed in said body and adapted to close said first communication passage first portion in response to said predetermined condition.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bushing type vibration insulator whose spring constant is changeable, usable as an engine mount, a cab mount, a body mount, a bushing or the like in an automotive vehicle.

2. Description of the Prior Art

For example, a bushing type vibration insulator to be used as a bushing of a suspension of an automotive vehicle requires a high spring constant for the purpose of improving driving stability of the vehicle. On the contrary, such a high spring constant of the bushing causes the vehicle to be uncomfortable to ride in when the vehicle runs on rough road, and additionally tends to provide so-called stuck state of road wheels so that the vehicle becomes difficult to get out of muddy road.

In view of this, a bushing type vibration insulator whose spring constant is variable has been proposed as disclosed, for example, in Japanese Utility Model Provisional Publication No. 60-66507. Such a vibration insulator consists of an elastic member disposed to connect an outer cylindrical member and an inner cylindrical member, the elastic member being made of an elastomeric material such as rubber. Two fluid chambers are formed between the outer and inner cylindrical members in such a manner as to be located in the diametrical direction of the cylindrical members. A part of each fluid chamber is defined by the elastic member. The fluid chambers are adapted to be simultaneously supplied with the fluid at a predetermined pressure by means of a pump and electromagnetic valves which are located remote from the two fluid chambers.

With such a bushing type vibration insulator, its spring constant is raised by increasing the fluid pressures of both the fluid chambers and lowered by decreasing the same fluid pressures. Thus, the vibration insulator improves vehicle comfortableness to drive in particularly during driving on rough road upon lowering the spring constant thereof, while sufficiently effectively preventing the stuck state of the wheels from occurrence.

However, since such a conventional bushing type vibration insulator is disposed remote from the hydraulic pump and the electromagnetic valves, fluid supply and discharge passages for fluidly connecting the vibration insulator and the pump are required to be considerably long. Accordingly, there is a high possibility of fluid leaking from the fluid supply and discharge passages while requiring a large space for installation of the vibration insulator and accessories therefor and extremely increasing the number of steps for production. Furthermore, it is required to provide a separate fluid tank for connecting the pump, the electromagnetic valves and the like.

In addition, because of the long fluid supply and discharge passages, a longer time is necessary to change over the rigidity value of the vibration insulator so as to be impossible to instantaneously change the characteristics of the vibration insulator. Furthermore, the dynamic spring constant of the vibration insulator cannot be suppressed to a lower value owing to line loss.

SUMMARY OF THE INVENTION

A bushing type vibration insulator of the present invention consists of an outer cylindrical member connected to a first member of a vibration system. The outer cylindrical member is connected through an elastic member with an inner cylindrical member which is disposed inside the outer cylindrical member sharing a common central longitudinal axis with the outer cylindrical member, and connected to a second member of the vibration system. At least two fluid chambers filled with a fluid are located between the outer and inner cylindrical members and defined by a part of the elastic member. The fluid chambers are communicated with each other through a communication passage which is closable by an actuator to block fluid communication between the fluid chambers under a predetermined condition.

Accordingly, when the actuator causes the communication passage to be opened to allow fluid flow between the fluid chambers, the spring constant of the vibration insulator is lowered to a desired low value. On the contrary, when actuator causes the communication passage to be closed to block fluid flow between the fluid chambers, the spring constant of the vibration insulator is increased to a desired high level.

Therefore, in case the vibration insulator is applied as a suspension bushing of an automotive vehicle, vehicle ride-in comfortableness during rough road cruising is greatly improved while effectively preventing stuck state of road wheels. Additionally, vehicle driving stability during high speed cruising can be sufficiently improved.

Furthermore, with this vibration insulator, the actuator may be installed directly to the inner or outer cylindrical member, and therefore the whole length of the communication passage is shortened. Consequently, space occupied by the vibration insulator and production steps of the vibration insulator are effectively reduced while removing possibility of leaking of the fluid through the communication passage. The shortened communication passage shortens a time required to change the spring constant of the vibration insulator while suppressing line loss to the minimum value thereby lowering the dynamic spring constant of the vibration insulator. Additionally, since fluid flow between the fluid chambers is controlled by the actuator, an oil pump and the space, production steps and cost therefore are not required.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following figures, like reference numerals designate corresponding elements and parts for the purpose of simplicity of illustration:

FIG. 1A is a vertical sectional view of a first embodiment of a bushing type vibration insulator according to the present invention;

FIG. 1B is a sectional view taken in the direction of arrows substantially along the line 1B--1B;

FIG. 1C is a side view of the vibration insulator of FIG. 1A;

FIG. 2 is a vertical sectional view similar to FIG. 1A but showing a second embodiment of a bushing type vibration insulator according to the present invention;

FIG. 3 is a vertical sectional view similar to FIG. 1A but showing a third embodiment of a bushing type vibration insulator according to the present invention;

FIG. 4A is a sectional view similar to FIG. 1B but showing a fourth embodiment of a bushing type vibration insulator according to the present invention;

FIG. 4B is a sectional view taken in the direction substantially along the line 4B--4B of FIG. 4A,

FIG. 5 is a sectional view similar to FIG. 1B but showing a fifth embodiment of a bushing type vibration insulator according to the present invention;

FIG. 6 is a sectional view of an essential part of a sixth embodiment of a bushing type vibration insulator according to the present invention;

FIG. 7A is a sectional view of an essential part of a seventh embodiment of a bushing type vibration insulator according to the present invention, showing an operational state of the vibration insulator;

FIG. 7B is a sectional view similar to FIG. 7A but showing another operational state of the vibration of FIG. 7A;

FIG. 8 is a sectional view similar to FIG. 1B but showing an eighth embodiment of a bushing type vibration insulator according to the present invention;

FIG. 9A is a vertical sectional view similar to FIG. 1A but showing a ninth embodiment of a bushing type vibration insulator according to the present invention;

FIG. 9B is a sectional view taken in the direction of arrows substantially along the line 9B--9B of FIG. 9A;

FIG. 10A is a vertical sectional view similar to FIG. 1A but showing a tenth embodiment of a bushing type vibration insulator according to the present invention;

FIG. 10B is a sectional view taken in the direction substantially along the line of 10B--10B;

FIG. 11 is a vertical sectional view similar to FIG. 1 but showing an eleventh embodiment of a bushing type vibration insulator according to the present invention;

FIGS. 12, 13, 14, 15 and 16 are sectional views similar to those of FIGS. 2, 3, 4B, 9B and 10A, respectively, but showing modified examples of the eleventh embodiment of FIG. 11;

FIG. 17 is a sectional view similar to FIG. 5 but showing a twelfth embodiment of a bushing type vibration insulator according to the present invention; and

FIG. 18 is a flowchart showing a process of operation of a displacement sensor used in the vibration insulator of FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Figs. 1A to 1C, there is shown a first embodiment of a bushing type vibration insulator in accordance with the present invention. The bushing type vibration insulator of this embodiment is designed to be used in a suspension system or vibration system of an automotive vehicle, and comprises an inner cylindrical member 1 connected to one member of the vibration system, and an outer cylindrical member 2 connected to another member of the vibration system. The inner cylindrical member 1 is coaxially disposed inside the outer cylindrical member 2, in which an elastic member 3 is disposed between the inner and outer cylindrical members 1, 2 to elastically connect the inner and outer cylindrical members 1, 2. The elastic member 3 is made of an elastomeric material such as rubber. Two fluid chambers to be filled with a fluid are formed between the inner and outer cylindrical members 1, 2 and located opposite in the diametrical direction.

The elastic member 3 is generally cylindrical and extends along the axis of the vibration insulator. The inner surface of the elastic member 3 is securely connected to the outer surface of the inner cylindrical member 1, for example, by adhesion upon vulcanization in case the elastic member is made of rubber. The outer surface of the elastic member 3 is securely connected to the inner surface of the outer cylindrical member 2 by putting an outer peripheral section 3b of the elastic member 3 between the outer cylindrical member inner surface and an intermediate cylindrical member 3a which is embedded in the elastic member 3 at the section near the outer peripheral surface. The outer peripheral section of the elastic member 3 forms an elastic member lining layer 3b for providing a fluid-tight seal between the elastic member 3 and the outer cylindrical member 2. The outer cylindrical member 2 is caulked or radially inwardly pressed to be rigidly connected with the intermediate cylindrical member 3a. The intermediate cylindrical member 3a is formed with two openings having the shape corresponding to the peripheral profile of each fluid chamber 4. The elastic member 3 is formed with two arcuate grooves at its central section in the axial direction. The two arcuate grooves 4A, 4A are located symmetrical with respect to a plane (not shown) containing an axis of the inner cylindrical member 1. Each groove 4A is opened upwardly to form an arcuate opening in the outer surface of the elastic member 3, so that the fluid chamber 4 is formed within each arcuate grooves 4A. Accordingly, the fluid chamber 4 is defined between the elastic member 3 and the outer cylindrical member 2. More specifically, the arcuate outer periphery of the fluid chamber 4 is defined by the inner surface of the outer cylindrical member; and the arcuate bottom and the opposite sides of the same fluid chamber 4 are defined by the bottom wall and the side walls of the groove 4A, thus maintaining secure fluid-tight seal of the fluid chambers 4, 4.

In this embodiment, the two fluid chambers 4, 4 are communicable with each other through a communication passage 5 which is adapted to be closable by means of an actuator 6 installed to the outer cylindrical member 2. The communication passage 5 includes first portions 5a, 5a which are formed between the outer cylindrical member 2 and the intermediate cylindrical member 3a. Each first portion 5a extends along the inner periphery of the outer cylindrical member 2, and has one end opened to the fluid chamber 4 and the other end communicated with a second portion 5b which is formed through the wall of the outer cylindrical member 2. The second portion 5b is communicated with a generally C-shaped third portion 5c which is formed in the body 6a of the actuator 6. The actuator body 6a is fixedly secured to the outer cylindrical member 2, for example, by welding. The actuator 6 has a spool 6c which is adapted to be driven to move forward (left in FIG. 1A) and backward (rightward in FIG. 1A) under the action of a solenoid coil 6b. The spool 6c is formed with a through-opening T which can be coincident or aligned with the third portion 5c of the communication passage 5 when the spool 6c is moved forward to take a position as indicated in FIG. 1A, so that the third portion 5c is put into its open state thereby to establish communication between the two fluid chambers 4, 4. It will be understood that the third portion 5c is put into its closed condition thereby to block communication between the two fluid chambers 4, 4 when the spool 6c is moved backward so that the through-opening T puts out of the position coincident with the third portion 5c. As shown, a fluid-tight seal is maintained between the second portions 5b and the third portion 5c of the communication passage 5 by means of O-rings disposed between the outer cylindrical member 2 and the actuator body 6a, thus preventing fluid leak from the connecting section of the first and second portions 5b, 5c.

The thus arranged bushing type vibration insulator is installed to the vibration system as follows: For example, the outer cylindrical member 2 is fitted into and fixed within a cylindrical bracket B provided at an end of a rod A connected to one member of the vibration system. Additionally, another member of the vibration system is connected to the inner cylindrical member 1. In case where the actuator 6 has been previously installed to the outer cylindrical member 2 as discussed above, the body 6a of the actuator 6 is pushed into a cut-out portion B.sub.1 of the cylindrical bracket B along the axis of the cut-out portion B.sub.1. The cut-out portion B.sub.1 extends from one end thereof to the vicinity of the other end in the axial direction of the cylindrical bracket B. Thus, the actuator 6 is located in position in the state where a major part of the actuator 6 projects over the outer peripheral surface of the cylindrical bracket B.

In addition, in case where the cylindrical bracket B is so designed that the actuator 6 is fixed in position by means of, for example, press-fit or caulking, the actuator 6 is fixed to the cylindrical bracket B after the outer cylindrical member 2 is fitted into and fixed within the cylindrical bracket B, thereby enabling suitable formation of the communication passage 5.

The manner of operation of the thus installed bushing type vibration insulator will be discussed hereinafter.

In the state where the spool 6c of the actuator 6 is moved forward to take the forward position as shown in FIG. 1A so that the communication passage 5 is opened to establish fluid communication between the two fluid chambers 4, 4, when upward and downward vibration as indicated by a two-headed arrow in FIGS. 1A to 1C is transmitted to the vibration insulator, the two fluid chambers 4, 4 alternately receive external forces in their compression and expansion directions so that the fluid within the fluid chambers 4, 4 flows from the high pressure side fluid chamber 4 through the communication passage 5 to the low pressure side fluid chamber 4. This causes the spring constant of the vibration insulator to be suppressed to a sufficiently low level.

In the state where the spool 6c is moved backward to take the backward position so that the communication passage 5 is closed to block the fluid communication between the two fluid chambers 4, 4, even when the upward and downward vibration is transmitted to the vibration insulator so that external forces in the compression and expansion directions alternatively act on the fluid chambers 4, 4, the fluid flow between the two fluid chambers 4, 4 is completely prevented, thus raising the spring constant of the vibration insulator to a sufficiently high level.

Accordingly, in case where the bushing type vibration insulator is used as a bushing of a suspension of an automotive vehicle, driving stability of the vehicle during high speed cruising is sufficiently improved upon closing the communication passage 5. On the contrary, ride-in comfortableness of the vehicle during rough road cruising is improved while effectively preventing the stuck state of the road wheels of the vehicle upon opening the communication passage 5.

FIG. 2 illustrates a second embodiment of the bushing type vibration insulator which is similar to the first embodiment of FIGS. 1A to 1C except for the shape of a section in which the communication passage 5 is formed. Also in this embodiment, the cylindrical bracket B is so designed that the actuator 6 is fixed in position by means of, for example, press-fit or caulking, in which the actuator 6 is fixed to the cylindrical bracket after the outer cylindrical member 2 is fitted into and fixed within the cylindrical bracket B, thereby enabling suitable formation of the communication passage 5. In this connection, the outer cylindrical member 2 and the intermediate cylindrical member 3a are flattened, for example, by squeezing or the like machining, in which fixing of the actuator 6 to the bracket B upon threading-into or the like after the outer cylindrical member 2 being fixed within the cylindrical bracket B is largely facilitated. Additionally, the fluid-tight seal between the outer cylindrical member and the actuator 6 is improved. These are the same as in case where the actuator 6 is directly fixed to the surface of the outer cylindrical member 2.

FIG. 3 illustrates a third embodiment of the bushing type vibration insulator according to the present invention, which is similar to the first embodiment of FIGS. 1A to 1C with the exception that the installation posture of the vibration insulator is shifted an angle of 90 degrees in which the actuator 6 is housed in the rod A. In this embodiment, the spring constant of the vibration insulator can be controlled to take high and low values against horizontal vibration as indicated by a two-headed arrow. Additionally, the actuator 6 is prevented from projecting over the cylindrical bracket B thereby effectively reducing a space occupied by the vibration insulator.

FIGS. 4A and 4B illustrate a fourth embodiment of the bushing type vibration insulator according to the present invention, which is similar to the first embodiment of FIGS. 1A to 1C with the exception that the actuator 6 is housed in the rod A in order